1. Field of the Invention
The present invention relates to an ink-jet recording ink set and an image forming method, and in particular, to a multi-liquid ink-jet recording ink set superior in fixing efficiency on various recording media including impermeable media and image reproducibility and an ink-jet recording method using the same.
2. Description of the Related Art
Ink-jet processes of ejecting ink from an ink-ejecting unit such as nozzle have been used in many printers, because they demand smaller space and are cheaper and allow non-contact image formation of recording media. Among many ink-jet processes, a piezo ink-jet process of ejecting ink by using deformation of a piezoelectric device and a thermal ink-jet process of ejecting ink by using the boiling phenomenon of ink under application of heat energy are characteristically superior in image definition and printing speed.
Currently, there is an urgent need for improvement in the processing speed and the image quality when an image is formed on an impermeable recording medium such as plain paper or plastic film in an ink-jet printer. Especially when a impermeable recording medium is used, elongation of drying of droplets after printing often leads to image bleeding and interference between ink droplets by mixing between neighboring ink droplets, making it difficult to form a sharp image (the interference between ink droplets is a phenomenon of neighboring ejected droplets fusing with each other for decrease in surface energy (for decrease in surface area). Fusion of neighboring droplets causes migration of the droplets, i.e., deviation of the droplets from the ejected positions, and thus, especially with an ink containing a colorant, fluctuation in line width when a thin line is drawn and irregularity of an image when the image is painted.).
Another problem known when an image is formed on an impermeable recording medium is that the fixing efficiency of the ink on recording medium is lower and the abrasion and water resistances are also lower.
As a method of accelerating hardening and fixing of ink on a recording medium for inhibition of image bleeding and improvement of fixing efficiency on the recording medium, a radiation-hardening ink-jet ink that is hardened not by evaporation of ink solvent but by irradiation with radiation ray was proposed in JP-A No. 10-323975.
However, even in such a case, it was not possible to prevent ejection interference occurring before radiation hardening.
Alternatively, proposed was an image forming method of printing an image by applying substantially water-free active light-hardening inks at least in four colors or more from ink-jet recording heads on a recording material, wherein an active light-hardening ink containing no colorant or a colorant in an amount of 1% or less is applied on a recording material at first and then, active light-hardening inks containing a colorant are applied (JP-A No. 2005-96254). Printing by the disclosed method occasionally resulted in spread of the droplets of the ink containing a colorant ejected on the ink containing no colorant and deterioration in the image sharpness.
Yet alternatively, an ink set consisting of a recording liquid containing a colorant and an ink spread suppressing liquid containing a component reactive with the component in the recording liquid was proposed in JP-A No. 2005-154767. Even with the ink set, it was difficult to form a high-definition image without ejection interference superior in fixing efficiency on an impermeable recording medium.
As described above, it was not possible to improve the fixing efficiency on impermeable recording media and prevent deterioration in image quality, for example by ejection interference, at the same time by conventional methods.